Oil being pumped from deep wells is quite warm and often contains wax compositions and various gases intermixed with the crude oil. As the oil is being pumped from deep in the ground to the surface, the oil is cooled by evolution and expansion of dissolved gases so that the waxes are cooled enough to deposit out onto the inner surface of the production tube through which the oil is exiting. The wax deposits on the inner surface of the oil well production tube in a reasonably well-defined zone. Deposition of the waxes ends at the point where sufficient gas has evolved to permit the wax deposition rate to drop below the value required to resist the scouring action of the flowing oil. Thus the process of wax deposition and build-up is reasonably stable. This waxing problem can be so serious as to substantially plug the production tube requiring shut down of the well, pulling of the pump plunger and physically removing the wax by mechanical brushing. Obviously, this is very expensive and output is reduced.
Oil wells have an inner pipe, or production tube, generally of steel, through which the oil exits and oil wells generally have a casing, or "oil string", surrounding the production tube, which is generally made of steel and which generally reaches down to the oil-bearing earth structure. There is thus provided annular space between the production tube through which the oil exits and the oil string casing.
It is the purpose of the invention to use the existing annulus, described above, thermal gradients along the length of the well, and a selected working fluid to prevent the deposition of wax on a continuous, self-controlled, basis.